Once I went for the HC4 I had made my mind up to have both backup and original drives on the single HC4 device. I'll just have to take my chance and hope nothing catastrophic happens that would take out both drives.
It's not the perfect backup solution but I guess "perfect is the enemy of the good" for me on this. Hopefully it will be good enough.
Thanks for your initial post. I did read it. It gives a good run through of a backup setup.
Well, the only thing you are protecting against with your current setup is:
a) One single HDD failure
b) An accidental delete that you notice very quickly
Scenarios that you do not protect against:
1) power surge (e.g. lightning strike)
2) accidental delete that you notice a year later
4) many others
What you could improve:
For 2) do versioned backups (borg-backup, rsnapshot)
For 3) ensure that only one drive is accessible from other machines. Use different credentials for your linux machine in combination with (2)
You could also later add an external drive and/or an offsite backup.
But if your data is valuable, I would not say that what you do today can be deemed "good" (in the sense of the enemy of the better). It is close to no protection, in my view.